Naturally occurring and synthetic waxes are extensively used in a wide cross-section of industries including the food preparation, pharmaceutical, cosmetic, and personal hygiene industries. The term wax is used to denote a broad class of organic ester and waxy compounds which span a variety of chemical structures and display a broad range of melting temperatures. Often the same compound may be referred to as either a "wax," "fat" or an "oil" depending on the ambient temperature. By whatever name it is called, the choice of a wax for a particular application is often determined by whether it is a liquid or solid at the temperature of the product with which it is to be used. Frequently it is necessary to extensively purify and chemically modify a wax to make it useful for a given purpose. Despite such efforts at modification, many physical characteristics of the waxes inherent in their structure still prevent them from being used successfully or demand that extensive additional treatments be undertaken.
For instance, extensive commercial use has been made of the naturally occurring carboxylic acids ("fatty acids") and their derivatives, most commonly the glyceryl derivatives in which all three hydroxy groups of the glyceryl molecule are esterified with a carboxylic acid. The carboxylic acids may be saturated or unsaturated. The tri-substituted glyceryls (triglycerides) are major components of most animal and plant fats/oils/waxes. When all three hydroxy groups of a glyceryl molecule have been esterified with the same fatty acid, it is referred to as a monoacid triglyceride. Whether one refers to triglycerides as "waxes," "fats," or "oils" depends upon the chain lengths of the esterified acids and their degree of saturation or unsaturation as well as the ambient temperature at which the characterization is made. Generally, the greater the degree of saturation and the longer the chain length of the esterified acids, the higher will be the melting point of the triglyceride.
An interesting feature of the triglycerides is that they may simultaneously solidify in more than one crystalline form within the same mass. This ability to exist in more than one crystalline state is termed "polymorphism" and is frequently observed among the waxes. Complicating the use of triglycerides even further is the fact that triglycerides exhibit a special form of polymorphism, designated monotropic polymorphism, in which the lower melting point crystal forms are unstable and convert over time to more stable forms, with the conversion dependent upon time and the temperature of the material. Monotropic polymorphism conversion always takes place in the direction towards the more stable crystal forms. Such conversion between polymorphic forms involves a structural rearrangement of the molecules.
For example, when melted, cooled, and solidified rapidly, the monoacid triglyceride glyceryl tristerate first hardens in a glass-like amorphous form which it then converts over time to a crystalline form (the alpha ".alpha." form) having a hexagonal crystal lattice structure with a melting point of about 54.degree. C. The polymorphic .alpha. form is only relatively stable. If heat is applied to .alpha. form material, the glyceryl tristerate will convert over time through an unstable intermediate form (the beta-prime ".beta.'" form) to a yet higher melting point form (the beta ".beta." form), having a triclinic crystal lattice structure with a melting point of about 72.degree. C. Once the conversion to the higher melting point .beta. form is complete, the .beta. form is stable. While many of the triglycerides, such as glyceryl tristerate, are available in relatively pure .beta. form powders, these .beta. forms are obtained from crystallization of the material from solvents into the powders. The powders themselves are usually not usable with processes which involve melting and resolidification since, once the triglyceride is melted and allowed to recrystallize, both the lower .alpha. and higher .beta. melting point polymorphs are present in the resulting material.
Such polymorphism presents problems in the formulation of products using triglyceride waxes as well as in the stability of the products over time. The commercial use of the polymorphic materials often requires extensive treatment of the product to convert the triglycerides to the .beta. form. If this is not done, the coexisting .alpha. and .beta. forms will slowly rearrange over time within the product to convert the material in the .alpha. form to material in the .beta. form. This rearrangement is both time and temperature dependent and may produce many undesirable features in the product. Thus, in preparation of such common foods as chocolates (to which triglycerides are added to affect the sense of taste), it is often necessary during processing to repeatedly cycle the temperature of the chocolate over a period of time to convert the residual c form triglycerides to .beta. form. If the temperature is not cycled, the chocolate may well show undesirable crystallization characteristics.
This "tempering" is a common feature of processes where polymorphic waxes and, in particular, triglycerides are used. Such tempering procedures must also take into account the characteristics of the compounds with which the waxes are mixed, presenting a complex problem of how to treat the entire mixture.
Similar problems arise when waxes are used as coating materials in encapsulation processes. Often the wax coating fails to shield the coated material as intended. An examination of the physical structure of such wax coats indicates that fissures and cracks develop in the coating. Certainly for the polymorphic waxes, the transition between polymorphic forms (with the associated structural rearrangement of the molecules into different crystal structures) is inconsistent with the coating/encapsulation requirement that the coating material posses a stable structure over time. Further, wax coatings containing both polymorphic forms tend to lack physical strength and be poor moisture barriers. Although polymorphic waxes may eventually convert substantially to the stable higher melting point form as they age in a warm environment, this process can take a long time, leaving sensitive materials inadequately protected by such wax coating or shell layer. A coating made of such waxes provides little immediate protection for sensitive materials.
Nowhere in the prior art is it known how to treat waxes so that they solidify in a more stable state or, in the case of polymorphic waxes, in the stable .beta. polymorphic form.